Phosphor For Light-emitting Diodes Research Articles

White light emission from NaLa(PO3)4: Dy3+ single-phase phosphors for light-emitting diodes

White light emission phosphors NaLa(PO3)4: Dy3+ were synthesized by a solid-state method. XRD analysis confirmed that all the Dy3+ doped phosphors are single phase. The photoluminescence excitation and emission spectra, concentration effect, decay property, and CIE coordinates were investigated. Strong excitation peaks of NaLa(PO3)4: Dy3+ were found around 350–400nm, which matched well with those of the near-UV LED chips. Under 350nm excitation the NaLa(PO3)4: Dy3+ exhibits intense white emission by combining the two emission peaks at 485nm and 571nm, attributed to the characteristic 4F9/2–6H15/2 and 4F9/2–6H13/2 transitions of Dy3+. The optimum doped concentration of Dy3+ ions is around 6mol% and the critical transfer distance of Dy3+ is calculated as 15.4Å. In addition, the CIE chromaticity coordinates of NaLa(PO3)4: Dy3+ phosphors are (0.2923,0.3359). The results indicate that the NaLa(PO3)4: Dy3+ phosphors have great potential as a single-component white-light-emitting phosphor for UV-light-emitting diodes.

A hybrid tool for spectral ray tracing simulations of luminescent cascade systems.

To perform adequate simulations of luminescent cascade systems, a hybrid method combining a commercial ray tracer and a programming tool is presented. True Monte Carlo algorithms for luminescent materials, treating each ray individually, are adapted to allow wavelength conversion of ray sets. Two solutions for the wavelength conversion of ray sets are discussed: a random approach, where absorption events are randomly selected to create emission events, and a combined approach, where information from multiple absorption events is combined to create emission events. Both methods are applied to simulate the performance of a virtual remote phosphor light-emitting diode module. When using the combined approach, the required computation time to achieve sufficient accuracy is a factor 2 lower, compared to the time required when applying the random approach.

Photoluminescence and thermal stability of yellow-emitting Na2Ba2Si2O7:Sm3+ phosphor for light-emitting diodes

A series of yellow-emitting Na2(Ba2−xSmx)Si2O7 phosphors have been prepared via solid-state reaction technique. X-ray diffraction (XRD), photoluminescence (PL) spectra, temperature-dependent luminescence property, concentration quenching mechanism and luminescence lifetime are applied to characterize the obtained samples. Under 402nm near ultraviolent excitation, the samples emit yellow light and the color purity is close to 100%. The critical quenching concentration of Sm3+ in the Na2Ba2Si2O7 host is about 3.6mol% and corresponding quenching behavior is ascribed to be electric dipole–dipole interaction. Furthermore, the phosphor has good thermal stability property, superior to the commercial yellow Y3Al5O12:Ce3+ phosphor and the activation energy for thermal quenching is calculated as 0.18eV.

Electrospinning preparation and luminescence properties of one-dimensional SrWO4: Sm3+ nanofibers

One-dimensional Sm3+ doped SrWO4 with or without different charge compensation approaches (co-doping Li+, Na+ and K+) nanofibers were prepared by electrospinning. The structure, morphology and luminescence properties of the obtained nanofiber phosphors were investigated. The X-ray diffraction, Fourier transformation infrared and thermogravimetric results show that the Sr(1−x)WO4: Smx3+ samples crystallize at 700 °C. Scanning electron microscope results indicate that as prepared nanofibers before/after calcination present uniform fiberlike morphology. The luminescence results show that Sr(1−x)WO4: Smx3+ phosphors can be excited efficiently by ultraviolet (UV) and near-UV light. The emission spectrum consists of three emission peaks at 561, 596 and 643 nm, corresponding to 4G5/2 → 6H5/2, 4G5/2 → 6H7/2 and 4G5/2 → 6H9/2 transitions of Sm3+, respectively. The optimal doping concentration of Sm3+ in SrWO4 is experimentally ascertained to be 4 mol%. The introduction of charge compensator R+ (R = Li, Na and K) can enhance the emission intensity of phosphors significantly. The co-doping of Li+ has the best compensation effect. The present investigation indicates that Sm3+ doped SrWO4 is a promising orange phosphor for light-emitting diode based on UV chip technology.

Power and photon budget of a remote phosphor LED module.

Light-emitting diodes (LEDs) are becoming increasingly important for general lighting applications. The remote phosphor technology, with the phosphor located at a distance from the LEDs, offers an increased extraction efficiency for phosphor converted LEDs compared to intimate phosphor LEDs where the phosphor is placed directly on the die. Additionally, the former offers new design possibilities that are not possible with the latter. In order to further improve the system efficiency of remote phosphor LEDs, realistic simulation models are required to optimize the actual performance. In this work, a complete characterization of a remote phosphor converter (RPC) consisting of a polycarbonate diffuser plate with a phosphor coating on one side via the bi-directional scattering distribution function (BSDF) is performed. Additionally, the bi-spectral BSDF which embraces the wavelength conversion resulting from the interaction of blue light with the RPC is determined. An iterative model to predict the remote phosphor module power and photon budget, including the recuperation of backward scattered light by a mixing chamber, is introduced. The input parameters for the model are the bi-spectral BSDF data for the RPC, the emission of the blue LEDs and the mixing chamber efficiency of the LED module. A good agreement between experimental and simulated results was found, demonstrating the potential of this model to analyze the system efficiency with errors smaller than 4%.

Spectral and surface investigations of Ca2V2O7:Eu3+ nanophosphors prepared by citrate-gel combustion method: a potential red-emitting phosphor for near-UV light-emitting diodes

In the present work, red-emitting Ca2V2O7:xEu3+ (x = 0.5–6.0 mol%) nanophosphors, in the form of powders, were synthesized by the citrate-gel combustion method using metal nitrates as precursors and citric acid as fuel. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy, photoluminescence (PL) and cathodoluminescence (CL) spectroscopy were used to study the structure, morphology and spectral properties of the samples. The chemical compositions and electronic states of the powders were analyzed with X-ray photoelectron spectroscopy. The average crystallite sizes estimated using the XRD data were found to be in the range of 30–45 nm, and were cross verified by TEM. The lattice parameters determined by the POWD program were approximated as a = 7.242 A, b = 6.674 A, c = 6.932 A and V = 291.24 A3, respectively. Under UV (395 nm) (PL) and electron (CL) excitation, the nanophosphors show characteristic emission from the Eu3+ ion (5D0 → 7Fj, j = 1–5) with the main peaks at 612 and 616 nm. The maximum emission intensity was recorded from the sample with an Eu3+ concentration of 4 mol% and a critical energy distance of 19.084 A between the donor and the acceptor. Above this concentration, there was a reduction in the intensity due to dipole–dipole induced concentration quenching effects. The potential applications of this phosphor as a high color-purity phosphor in light-emitting diodes are evaluated.

Measuring, simulating and optimizing current LED phosphor systems to enhance the visual quality of lighting

Lighting engineering aspects of light emitting diodes (LEDs) with down converting phosphors (phosphor converted LEDs or PC-LEDs) were investigated by building sample PC-LEDs, measuring their spectral emission physically and simulating them with a software. This article describes the influence of the phosphors’ chemical, physical and technological properties on some well-established and widely used measures of visual lighting quality including luminous efficacy and the color rendering index. The dependence of these measures on YAG and LuAG phosphor particle size and activator concentration in the PC-LEDs is dealt with. Light sources of superior lighting quality can be obtained by mixing several phosphors. Hence, the mixture of a green and red phosphor system was also studied for a set of real PC-LED light sources and their simulations. Two green and two red phosphors are considered in this study. To predict and optimize the lighting quality of PC-LEDs with a reasonable accuracy, a usable input shall be provided for the simulation software assuming the understanding of the emission mechanisms. To validate our simulation results, the PC-LEDs’ measured spectral emission characteristics were compared with their simulated counterparts. The measurement and simulation of spectral power distributions contribute to the understanding of new phosphor mixtures. The present simulation method turned out to be usable to optimize the target parameters of the PC-LED (luminous efficacy, white tone quality and color quality of the illuminated colored objects).

Preparation and investigation of Ca2.96(P0.99B0.01O4)2:0.04Dy3+ single-phase full-color phosphor

Novel single-phased white-light-emitting Ca2.96(P0.99B0.01O4)2:0.04Dy3+ phosphors for light-emitting diode (LED) applications were synthesized by conventional solid-state reactions. The phases and luminescent properties of the obtained Ca2.96(P0.99B0.01O4)2:0.04Dy3+ phosphors were well characterized. The results show that the excited bands of Ca2.96(P0.99B0.01O4)2:0.04Dy3+ phosphor centered at wavelengths of 324nm (6H15/2→4M17/2), 350nm (6H15/2→4M15/2, 6P7/2), 366nm (6H15/2→4I11/2), 387nm (6H15/2→4I13/2, 4F7/2), 427nm (6H15/2→4G11/2), and 448nm (6H15/2→4I15/2). On excitation at 350nm, the emission transitions of Dy3+ consisted of double emission bands, which can be assigned to the transition emissions of 4F9/2→6H15/2 (480nm) and 4F9/2→6H13/2 (572nm). One mol% B3+ dopant improved the luminescence intensity of Ca2.96(PO4)2:0.04Dy3+ phosphor, and the reason was proposed. The developed phosphor has great potential as a single-component white-light-emitting phosphor for UV-light-emitting diodes.

Rare-Earth Elements in Lighting and Optical Applications and Their Recycling

Rare-earth elements (REEs) are used in lighting and optical applications to enable color and light adjustment, miniaturization, and energy efficiency. Common applications of REEs include phosphors for light-emitting diodes, lasers, and electronic video displays. This article reviews how REEs are widely used in these applications. However, supply constraints, including rising prices, environmental concerns over mining and refining processes, and China’s control over the supply of the vast majority of REEs, are of concern for manufacturers. In view of these supply constraints, this article discusses ways for manufacturers of lighting and optical devices to identify potential substitutes and recycling methods for REEs.

Simple digital FIR equalizer design for improving the phosphor LED modulation bandwidth in visible light communication

We propose and demonstrate a simple digital post-equalization technique to improve the bandwidth-limitation of light-emitting-diode (LED) visible-light-communication (VLC) channel. The design of finite-impulse-response equalizer according to the channel response is presented to improve the bandwidth limitation of LED VLC channel. Here, no optical blue filter is used. The simulation and experimental results show \(\sim \)10 times enhancement of the direct modulation speed of white-light LED VLC system. When compares with the previous demonstration using high-pass equalization circuit constructed by lumped capacitor and resistor, the proposed scheme shows an improvement in signal quality and transmission distance, and a 10 Mbit/s error-free free-space transmission over 1 m can be achieved under the bit error rate of \(< 10^{-9}\).

Metal–Organic Framework Luminescence in the Yellow Gap by Codoping of the Homoleptic Imidazolate ∞3[Ba(Im)2] with Divalent Europium

The rare case of a metal-triggered broad-band yellow emitter among inorganic-organic hybrid materials was achieved by in situ codoping of the novel imidazolate metal-organic framework ∞(3)[Ba(Im)2] with divalent europium. The emission maximum of this dense framework is in the center of the yellow gap of primary light-emitting diode phosphors. Up to 20% Eu2+ can be added to replace Ba2+ as connectivity centers without causing observable phase segregation. High-resolution energy-dispersive X-ray spectroscopy showed that incorporation of even 30% Eu2+ is possible on an atomic level, with 2-10% Eu2+ giving the peak quantum efficiency (QE = 0.32). The yellow emission can be triggered by two processes: direct excitation of Eu2+ and an antenna effect of the imidazolate linkers. The emission is fully europium-centered, involving 5d → 4f transitions, and depends on the imidazolate surroundings of the metal ions. The framework can be obtained by a solvent-free in situ approach starting from barium metal, europium metal, and a melt of imidazole in a redox reaction. Better homogeneity for the distribution of the luminescence centers was achieved by utilizing the hydrides BaH2 and EuH2 instead of the metals.

Formation condition of red Ce^3+ in Ca_3Sc_2Si_3O_12:Ce^3+, N^3− as a full-color-emitting light-emitting diode phosphor

In this Letter, we study diffuse reflectance and photoluminescence spectra for O(2-) fully coordinated green-emitting Ce(3+) and N(3-) partially coordinated red Ce(3+) in Ca(3)Sc(2)Si(3)O(12)(CSS):Ce(3+), N(3-) as a function of CeO(2) and Si(3)N(4) contents in the raw material. Our results indicate that the presence of N(3-) can enhance Ce(3+) solubility in the form of red centers in CSS. At low Ce(3+) concentration, green Ce(3+) forms preferentially while red Ce(3+) hardly forms even if N(3-) content in the raw material is sufficient. There exists a threshold concentration of green Ce(3+); only beyond that can color tunable luminescence with enriched red emission be achieved. Energy transfer from green Ce(3+) to red Ce(3+) is also studied, as only the green Ce(3+) is excited by blue light.

Ligand field density functional theory calculation of the 4f2 → 4f15d1 transitions in the quantum cutter Cs2KYF6:Pr3+

Herein we present a Ligand Field Density Functional Theory (LFDFT) based methodology for the analysis of the 4f(n)→ 4f(n-1)5d(1) transitions in rare earth compounds and apply it for the characterization of the 4f(2)→ 4f(1)5d(1) transitions in the quantum cutter Cs2KYF6:Pr(3+) with the elpasolite structure type. The methodological advances are relevant for the analysis and prospection of materials acting as phosphors in light-emitting diodes. The positions of the zero-phonon energy corresponding to the states of the electron configurations 4f(2) and 4f(1)5d(1) are calculated, where the praseodymium ion may occupy either the Cs(+)-, K(+)- or the Y(3+)-site, and are compared with available experimental data. The theoretical results show that the occupation of the three undistorted sites allows a quantum-cutting process. However size effects due to the difference between the ionic radii of Pr(3+) and K(+) as well as Cs(+) lead to the distortion of the K(+)- and the Cs(+)-site, which finally exclude these sites for quantum-cutting. A detailed discussion about the origin of this distortion is also described.

Synthesis and color-tunable luminescence properties of Eu2+ and Mn2+-activated Ca3Mg3(PO4)4 phosphor for solid state lighting

Eu2+ and Mn2+ singly doped and Eu2+/Mn2+-co-doped Ca3Mg3(PO4)4 phosphors are prepared by the conventional solid-state method. The Ca3Mg3(PO4)4:Eu2+,Mn2+ phosphors are efficiently excited at wavelengths ranging from 200 to 430 nm, which can match well with near ultraviolet (UV) light emitting diode (LED) chips. As a result of fine-tuning of the emission composition of the Eu2+ and Mn2+ ions, white light emission can be realized by combining the emission of Eu2+ and Mn2+ in a single host lattice under UV light excitation. Resonant energy transfer with an efficiency value of over 90% from the Eu2+ to Mn2+ ions is demonstrated to be in the dipole-quadrupole mechanism in such system and the energy transfer efficiency increases with an increase of the Mn2+ doping content, which is confirmed by the luminescence spectra and fluorescence decay curves, respectively. The energy transfer critical distance has been calculated and evaluated by both the concentration quenching and spectral overlap methods. These results indicate that the Ca3Mg3(PO4)4:Eu2+,Mn2+ phosphors have potential applications as a near UV-convertible phosphor for light-emitting diodes because of its broad excitation in the near-ultraviolet range and the efficient emission light.

Thermal quenching at the microscopic level in multi-phase thiosilicate phosphors

Europium (Eu2+) doped calcium thiosilicate (Ca2SiS4) is interesting as conversion phosphor for light-emitting diodes (LEDs), because of its yellow-to-red emission, depending on the europium concentration. However, for elevated europium concentrations two phases appear which is reflected in the temperature dependency of the emission spectrum. In this work we study the emission spectrum and thermal quenching behaviour at the microscopic level, by performing temperature dependent cathodoluminescence spectroscopy in a scanning electron microscope. A clear relation between the local europium concentration and the thermal quenching is obtained. This proves useful to explain the luminescence properties of the bulk phosphor.

Blue Light-Emitting Diode Phosphors Based upon Oxide, Oxyhalide, and Halide Hosts

In this article, we describe various oxide, oxyhalide, and halide phosphors that can be used in combination with blue light emitting diodes (LEDs) for lighting and display systems. Within specific host-activator combinations, we briefly discuss composition-property relationships and the potential impact upon LED system performance. In addition, some of the practical drawbacks and open issues for many of these materials are discussed, giving potential routes for future work.

Effect of composition on the luminescence of Ce3+ activated Sr3AlO4F phosphor for light-emitting diode

A series of Ce3+ activated Sr3AlO4F phosphors were synthesized by a high-temperature solid-state method. The Ce3+ ions occupy two distinct Sr2+ sites in the host. The phosphors exhibit strong absorption in the spectral range of near-UV to blue light with a maximum at ∼400nm. The emission color may be efficiently tuned by controlling the composition of phosphor, which is interpreted in terms of the site occupancy, energy transfer and crystal structure. The results show that the phosphor is a potential light-emitting diode (LED) phosphor.

A Study on the Luminescence and Energy Transfer of Single-Phase and Color-Tunable KCaY(PO4)2:Eu2+,Mn2+ Phosphor for Application in White-Light LEDs

Novel single-phased white light-emitting KCaY(PO(4))(2):Eu(2+),Mn(2+) phosphors for light-emitting diode (LED) applications were synthesized by conventional solid-state reaction. The emission hue could be controlled by tuning the Eu(2+)/Mn(2+) ratio via the energy transfer; the the emission hue of KCaY(PO(4))(2):Eu(2+),Mn(2+) varied from blue (0.1853, 0.2627) to white-light (0.3350, 0.3203) and eventually to purple (0.3919, 0.2867). The mechanism of energy transfer from a sensitizer Eu(2+) to an activator Mn(2+) in KCaY(PO(4))(2):Eu(2+),Mn(2+) phosphors was demonstrated to be an electric dipole-quadrupole interaction. Combining a NUV 405-nm chip and a white-emitting KCaY(PO(4))(2):1%Eu(2+),4%Mn(2+) phosphor produced a white-light NUV LED, demonstrating CIE chromaticity coordinates of (0.314, 0.329) and a color temperature of 6507 K.

The Influence of the Thermal Effect on CdSe/ZnS Quantum Dots in Light-Emitting Diodes

This study investigates the effect of temperature on CdSe/ZnS quantum dots (QDs) in GaN-based light-emitting diodes (LEDs) using the phosphor conversion efficiency (PCE) and LED junction temperature. In our simulation, the blue chip and CdSe/ZnS QDs temperature are similar because of their minimal thickness. Furthermore, to verify the effect of temperature on CdSe/ZnS QDs, we use continuous wave and pulsed current sources to measure the relationship between the temperature and relative PCE. Higher junction temperatures are observed with greater CdSe/ZnS QD volume in LEDs. This is attributed to the thermal conduction and nonradiative energy between CdSe/ZnS QDs and blue chip. Therefore, if thermal management is improved, CdSe/ZnS QDs are expected to be used as color converting material in LEDs.

69.2: WITHDRAWN: 69.3: Invited Paper: Current Issues in Quantum Dot Phosphors for Light‐Emitting Diodes

AbstractCurrently, light‐emitting diodes with quantum dots (QDs) wavelength converter show excellent luminescence property (∼65 lm/W, CRI &gt; 90), demonstrating them as one of ideal phosphor. Here, we will discuss historical archives on development of QD phosphors and current issues such as environmental hazard, interfacial problem between QDs and encapsulants, and their degradation.